Human-machine interfaces are used in myriad industries to translate human movements to machine movements. For example, some aircraft flight control systems include a human-machine interface in the form of a control stick, sometimes referred to as a side stick. The flight control system, in response to input forces supplied to the human-machine interface from the pilot, controls the movements of various aircraft flight control surfaces. No matter the particular end-use system, the human-machine interface preferably includes some type of haptic feedback mechanism back through the interface to the interface operator.
Many haptic feedback mechanisms are implemented using one or more force sensors as the primary input device to the feedback loop. In some instances, the force sensors are coupled to a part that deflects when a user supplies an input force to the human-machine interface. The forces sensors, upon deflection of the part, supply force signals representative of the input force to a control, which in turn controls current supplied to a motor. The motor, which is coupled to the human-machine interface, for example via a gearbox, supplies a feedback force to the user interface. Although these types of haptic feedback mechanisms are generally safe and reliable, they do suffer certain drawbacks. For example, because it is postulated that the user interface could be inadvertently overloaded, the part to which the force sensors are coupled is typically manufactured relatively robustly, which can increase overall cost.
Hence, there is a need for human-machine interface that provides relatively low cost overload protection of the force sensors. The present invention addresses at least this need.